1. Field of the Invention
The present invention relates to non-impact printing apparatus and method for recording using printheads having a plurality of recording elements such as light-emitting diodes (LEDs) or the like.
2. Brief Description of the Prior Art
In electrophotographic recorders using a fixed sized dot low resolution output printer, the smoothness of text and line graphics suffers due to line raggedness of near vertical and near horizontal lines. To reduce the "scalloped" effect on the near vertical and horizontal lines, one can increase the printing resolution (or dpi) of the writing system (but typically this entails much higher costs). Another way to do this is to use multiple dot sizes that can be done with a grey level LED printhead either via multi-bit pulsewidth modulation (PWM) methods such as proposed in U.S. Pat. No. 4,750,010 or binary multiple address printing methods such as proposed in U.S. Pat. No. 5,138,337. But there is a limit on the dot size variation (dynamic range between maximum and minimum size) due to exposure emitter size constraints, MTF of the lens and the toner's capability to carry a very small dot by itself. Therefore, it is desirable to be able to shift the centroids of the exposure dots or pixels so that smaller size dots can be placed closer to other larger dots for process stability reasons. Also, one can get a better dot edge placement at the same time. One way to do this is to use multiple address printing methods in either a binary printhead or just a regular multiple-bit printhead running in the multiple address mode; see for example U.S. Pat. No. 5,025,322. Since the data for every sub-line has to be reloaded in the multiple address mode, the printing speed of the system is usually slower. One can speed that up with multiple input data lines, but cost and the size of the system goes up significantly. Therefore, it is desirable and an object of the invention to provide a printer apparatus and method that is adapted to record multiple dot sizes, have centroid shift capability to enhance rendition and have a faster data loading capability for use with higher speed recording systems.